As explained here [1], Django currently only supports hashes in the form <algorithm>$<iterations>$<salt>$<hash>. There is also a note about bcrypt [2] that explicitely tells about incompatibility of such hashes (starting with $), and even suggests updating hashes in the database.

In 1.5, you could create a custom user model and customize check_password to pass a modified hash to the hashers.check_password function.

What Django could do in the future (need to be confirmed by a security-savvy developer) is to pass hashes to the hashers who could determine themselves if they support the hash format (in identify_hashers). Marking as DDN for this idea.

As for me, I think that custom user model is orthogonal to custom hashers functionality. The idea here is to give more flexibility to the password hashers system, and not hard code the hash starting with $algorithm$....
I even think that asking people having to cope with custom password hashes to rewrite the password checking mechanism instead of simply creating their own hasher has security implications, as they might easily introduce flaws in this sensible part of their code.